Commercial deals concluded by the Ukraine during the presidency of Viktor Yanukovich are coming under scrutiny, with the spotlight trained especially on lucrative gas projects involving Western companies.

The country's acting prosecutor general has said he will review contracts for evidence of corrupt practices.

Some members of the Ukrainian parliament have called for the new government to examine how, without significant financial outlay, a small Kiev-based consultancy received interests in shale gas projects led by Shell and Chevron and said to be worth hundreds of millions of dollars.

The parliamentarians said they had no evidence of wrongdoing, but wanted to understand how geological consultancy SPK-GeoService, founded by three former employees of state oil and gas company Naftogaz, was awarded 10% stakes in two shale deposits, Yuzivska and Olesska, owned by another state oil and gas group, Nadra Ukrayny, in return for helping to bring the fields on stream.

Shell and Chevron entered the ventures in 2013, promising to spend hundreds of millions of dollars on exploration in return for their stakes, the news agency Reuters noted.

Sergiy Stovba, research director at GeoService, denied that the consultancy had received an excessively generous deal as well as denying any connection between the firm and the Yanukovich regime.